The present invention relates to a control apparatus and a control method a negative pressure actuator used, for example, for opening and closing an intake control valve in an engine, which is operated by an intake negative pressure stored in a negative pressure tank as a power source.
Heretofore, there has been known a negative actuator comprising a negative pressure tank storing an intake negative pressure in an engine, a diaphragm type actuator which is operated by a negative pressure stored in the negative pressure tank as a power source, a valve which is driven to open and close by the actuator, and a solenoid valve which switching controls between supply of the negative pressure and supply of an atmospheric pressure to the actuator, wherein the opening and closing of the valve is controlled by controlling the power supply to the solenoid valve (refer to Japanese Unexamined Patent Publication No. 7-189708).
Since the negative pressure in the negative pressure tank is released when the engine intake negative pressure is reduced, the negative pressure actuator is permitted to operate only when the engine intake negative pressure exceeds an operating possible negative pressure of the negative pressure actuator.
However, even if the intake negative pressure exceeds the operating possible negative pressure to approach the atmospheric pressure, the negative pressure in the negative pressure tank is not released at once and a time delay exists for the negative pressure in the negative pressure tank to become smaller than the operating possible negative pressure.
Therefore, in such an arrangement as mentioned above, the operation of the negative pressure actuator is prohibited although the negative pressure of sufficient amount is stored in the negative pressure tank.
The present invention has an object to provide a control apparatus and a control method of a negative pressure actuator, capable of using a negative pressure in a negative pressure tank to the most possible extent to operate the negative pressure actuator.
In order to achieve the above object, the present invention is constructed to calculate an operating possible time of a negative pressure actuator based on an engine operating condition, and to permit the operation of the negative pressure actuator if it is within the operating possible time, while prohibiting the operation of the negative pressure actuator if the operating possible time is exceeded.
The present invention is also constructed to calculate a negative pressure in a negative pressure tank based on an engine operating condition, and to permit the operation of the negative pressure tank if the calculated negative pressure is greater than a threshold value, while prohibiting the operation of the negative pressure actuator if the calculated negative pressure is less than the threshold value.
Other objects and features of this invention will be understood from the following description with reference to the accompanying drawings.